In general, a pipe that transports a fluid in liquid or gaseous form must especially withstand the pressure, temperature and corrosiveness of the transported fluid, on the one hand, and the corrosiveness of the surrounding medium, on the other hand.
In the case of an air intake pipe for a turbocompressed motor vehicle engine, the fluid is hot air at a pressure of about 1.5 to 2 bar and at a temperature of about 100° C. to 200° C., and this hot air is charged with oil (in particular oil used to lubricate the turbocompressor), which makes it necessary to ensure that the inner layer of this pipe satisfactorily withstands the aggressive nature of the oil. Moreover, as the temperature under the engine cowl tends to increase more and more, the air intake pipe must withstand an external temperature of about 150° C.
To obtain such resistance, use is generally made of inner and outer layers for this pipe that are both made of elastomeric materials based on ethylene-acrylic acid copolymers (abbreviated as AEM, in particular VAMAC®) crosslinkable with an amine or a peroxide, or alternatively copolymers of an acrylate and of a comonomer providing reactive sites for crosslinking with sulfur or with an amine (abbreviated as ACM).
Also in a known manner, these air intake pipes are reinforced with ribbed fabric that is arranged between these inner and outer layers and that is usually formed from multifilaments of m-aramid (aromatic polyamide), which gives the pipe excellent resistance to high external temperatures. However, m-aramid has the drawback of penalizing the overall manufacturing cost of the pipe when compared with PET (polyethylene terephthalate) especially, which is a much less expensive material.
Document EP-A1-1 334 995 presents a pipe, for example for an air intake circuit at the outlet of a turbocompressor, which may comprise, between these inner and outer layers, a reinforcement made of PET and an intermediate layer intercalated between the inner layer and this reinforcement, it being pointed out that the intermediate and outer layers in contact with the PET are both specifically based on an ACM or an AEM that comprises carboxyl reactive sites and that is crosslinked with an amine. More specifically, the crosslinking system chosen for these two layers comprises a diamine as crosslinking agent and a guanidine coupled to a guanidine derivative chelated with a metal as crosslinking promoter, which prevents the known deterioration by aminolysis of PET in contact with ACM or AEM crosslinked with an amine.
A major drawback of the pipe presented in that document lies in the choice of this complex and expensive crosslinking system in relation with the ACM or AEM elastomer bearing sites that are necessarily carboxyls, and in the resulting relatively high manufacturing cost for the pipe.